• Reversible airway obstruction is defined as an increase of ≥12% and ≥200 ml in FEV1 over the patient's pre-bronchodilator value in litres within 10-15 minutes after inhaling a total of 360 µg of albuterol or 400 µg salbutamol via MDI (metered dose inhaler) (reversibility test). The administration of albuterol or salbutamol for the reversibility test is to be within 30 minutes after pre-bronchodilator spirometry.